1. Field of the Invention
This invention relates to circuit breakers for protecting electric power circuits. More particularly, it relates to a set of secondary contacts which can be remotely controlled, but can be manually closed at the breaker. It further relates to such a circuit breaker with an indicator which provides an indication of the open/closed state of the set of secondary contacts.
2. Background Information
Circuit breakers used in residential and light commercial applications are commonly referred to as miniature circuit breakers because of their limited size. Such circuit breakers typically have a pair of separable contacts opened and closed by a spring powered operating mechanism. A thermal-magnetic trip device actuates the operating mechanism to open the separable contacts in response to persistent overcurrent conditions and to short circuits. Usually, circuit breakers of this type for multiple circuits within a residence or commercial structure are mounted together within a load center which may be located in a basement or other remote location. In some applications, it has been found convenient to use the circuit breakers for other purposes than just protection, for instance, for load shedding. It is desirable to be able to perform this function remotely, and even automatically, such as with a computer. However, the spring powered operating mechanisms are designed for manual reclosure and are not easily adapted for reclosing remotely. In any event, the mechanisms are not designed for repeated operation over an extended period of time.
U.S. Pat. Nos. 5,301,083 and 5,373,411 describe a remotely operated circuit breaker which introduces a second pair of contacts in series with the main separable contacts. The main contacts still interrupt overcurrents, while the secondary contacts perform the discretionary switching operations. The secondary contacts are controlled by a solenoid which is spring biased to close the contacts. The solenoid has two coils, an open coil and a hold coil. Initially, both coils are energized to open the contacts. Power to the open coil is then turned off, and only the hold coil remains energized. Thus, continuous power is required to keep the main contacts open. When power to the hold coil is terminated, the spring recloses the secondary contacts. Commonly owned, concurrently filed U.S. Patent Application identified by Attorney Docket No. 99-PDC-269 discloses a magnetically latchable solenoid which only requires momentary power to switch between the open and closed states. In both of these remotely operated circuit breakers, the secondary contacts are not controllable at the circuit breaker. They can only be controlled by the remotely generated signals. There are times when it is desirable to place the circuit breaker back in service from the location of the circuit breaker. The main contacts can be reclosed by the handle provided on the circuit breaker, but this does not close the secondary contacts. It is also desirable to be able to determine the status of the secondary contacts of the remotely operated circuit breaker. Again, the handle indicates the position of the main contacts, but indicates nothing with respect to the secondary contacts.
Accordingly, there is a need for an improved remotely operated circuit breaker.
More particularly, there is a need for such a circuit breaker having remotely controllable secondary contacts which can also be controlled at the circuit breaker.
There is also a need for such a remotely operated circuit breaker which provides at the circuit breaker an indication of the open/closed state of the secondary contacts.